[libFuzzer] mutation: insert the size of the input in bytes as one of the ways to mutate a binary integer

llvm-svn: 284909

2 files changed, 21 insertions, 11 deletions

diff --git a/llvm/lib/Fuzzer/FuzzerMutate.cpp b/llvm/lib/Fuzzer/FuzzerMutate.cpp
index d38ee22ef51..7da9256c562 100644
--- a/llvm/lib/Fuzzer/FuzzerMutate.cpp
+++ b/llvm/lib/Fuzzer/FuzzerMutate.cpp
@@ -299,15 +299,21 @@ size_t ChangeBinaryInteger(uint8_t *Data, size_t Size, Random &Rand) {
   size_t Off = Rand(Size - sizeof(T) + 1);
   assert(Off + sizeof(T) <= Size);
   T Val;
-  memcpy(&Val, Data + Off, sizeof(Val));
-  T Add = Rand(21);
-  Add -= 10;
-  if (Rand.RandBool())
-    Val = Bswap(T(Bswap(Val) + Add));  // Add assuming different endiannes.
-  else
-    Val = Val + Add;                   // Add assuming current endiannes.
-  if (Add == 0 || Rand.RandBool())     // Maybe negate.
-    Val = -Val;
+  if (Off < 64 && !Rand(4)) {
+    Val = Size;
+    if (Rand.RandBool())
+      Val = Bswap(Val);
+  } else {
+    memcpy(&Val, Data + Off, sizeof(Val));
+    T Add = Rand(21);
+    Add -= 10;
+    if (Rand.RandBool())
+      Val = Bswap(T(Bswap(Val) + Add)); // Add assuming different endiannes.
+    else
+      Val = Val + Add;               // Add assuming current endiannes.
+    if (Add == 0 || Rand.RandBool()) // Maybe negate.
+      Val = -Val;
+  }
   memcpy(Data + Off, &Val, sizeof(Val));
   return Size;
 }
diff --git a/llvm/lib/Fuzzer/test/FuzzerUnittest.cpp b/llvm/lib/Fuzzer/test/FuzzerUnittest.cpp
index 118ae57cb78..79b8c2865f6 100644
--- a/llvm/lib/Fuzzer/test/FuzzerUnittest.cpp
+++ b/llvm/lib/Fuzzer/test/FuzzerUnittest.cpp
@@ -491,6 +491,8 @@ void TestChangeBinaryInteger(Mutator M, int NumIter) {
   uint8_t CH3[8] = {0x00, 0x11, 0x2a, 0x33, 0x44, 0x55, 0x66, 0x77};
   uint8_t CH4[8] = {0x00, 0x11, 0x22, 0x33, 0x44, 0x4f, 0x66, 0x77};
   uint8_t CH5[8] = {0xff, 0xee, 0xdd, 0xcc, 0xbb, 0xaa, 0x99, 0x88};
+  uint8_t CH6[8] = {0x00, 0x11, 0x22, 0x00, 0x00, 0x00, 0x08, 0x77}; // Size
+  uint8_t CH7[8] = {0x00, 0x08, 0x00, 0x33, 0x44, 0x55, 0x66, 0x77}; // Sw(Size)
 
   int FoundMask = 0;
   for (int i = 0; i < NumIter; i++) {
@@ -502,8 +504,10 @@ void TestChangeBinaryInteger(Mutator M, int NumIter) {
     else if (NewSize == 8 && !memcmp(CH3, T, 8)) FoundMask |= 1 << 3;
     else if (NewSize == 8 && !memcmp(CH4, T, 8)) FoundMask |= 1 << 4;
     else if (NewSize == 8 && !memcmp(CH5, T, 8)) FoundMask |= 1 << 5;
+    else if (NewSize == 8 && !memcmp(CH6, T, 8)) FoundMask |= 1 << 6;
+    else if (NewSize == 8 && !memcmp(CH7, T, 8)) FoundMask |= 1 << 7;
   }
-  EXPECT_EQ(FoundMask, 63);
+  EXPECT_EQ(FoundMask, 255);
 }
 
 TEST(FuzzerMutate, ChangeBinaryInteger1) {
@@ -581,7 +585,7 @@ TEST(Corpus, Distribution) {
   Random Rand(0);
   InputCorpus C("");
   size_t N = 10;
-  size_t TriesPerUnit = 1<<20;
+  size_t TriesPerUnit = 1<<16;
   for (size_t i = 0; i < N; i++)
     C.AddToCorpus(Unit{ static_cast<uint8_t>(i) }, 0);